This application is related to copending application Ser. No. 07/404,028, filed on Sep. 6, 1989, now abandoned.
1. Field of the Invention
The present invention relates to phenol terminated diester compositions derived from dicarboxylic acid, polyester or alkyd backbone materials, to solid crosslinked polymer compositions prepared therefrom, and to methods for improving coating properties of films and surface coatings based thereon. It also relates to methods for preparing such materials containing phenolic terminal end cap groups.
2. Description of the Related Art
Coating formulations usually contain a number of components. A primary component is a resin which can be natural or synthetic. The resin acts as a polymeric coating binder or polymeric coating vehicle for the coating formulation. In addition, most coatings require a solvent, and the coating may also contain a wide variety of additives. Further, many coatings also contain a crosslinking agent, which after application of the coating vehicle to a substrate, reacts chemically with the resin during a curing stage to produce a film containing a crosslinked network. The crosslinked network is necessary for the production of good film properties. The curing stage can be conducted at ambient conditions ("aiz.-dry system"), or at elevated temperatures ("baked system"). In either case, the solvent is evaporated during the curing stage, resulting in a coating film. A number of properties are important for the coating film, including hardness, flexibility, weather resistance (weatherability), chemical resistance, solvent resistance, corrosion resistance, adhesion to various substrates, and impact resistance. The properties depend on may factors including type, molecular weight, monomer composition, and glass transition temperature (Tg) of the resin; type and amount of the crosslinker; curing conditions; curing catalyst; and additives. Variations of these parameters can be used to create a wide range of differences in film properties to fit requirements for a number of diverse applications. However, it is not always possible to optimize all of the desirable properties simultaneously.
For example, hardness and impact resistance are two desirable characteristics of coatings which are somewhat mutually exclusive since high hardness is usually associated with films having high Tgs and low flexibility. Conversely, high impact resistance is associated with films having low Tgs and high flexibility. This necessitates a trade-off between high hardness and high impact resistance. It is frequently possible to optimize one of these properties, but at the expense of the other.
In European Patent Application No. 0 287 233 filed Mar. 28, 1988, and published Oct. 19, 1988, Jones et al. teach a method to simultaneously obtain both high hardness and high impact resistance in a coating by employing liquid crystalline (L.C.) polymers. The L.C. polymers are characterized as containing mesogenic groups which impart the L.C. character to the polymer. The mesogenic groups are chemical structures that contain a rigid sequence of at least two, and frequently more, aromatic rings connected in the meta or para position by a covalent bond or by other rigid or semirigid chemical linkages. In addition to the mesogenic groups, the polymers contain conventional polymeric units which are attached to the mesogens via a covalent bond.
Jones formulates these L.C. polymers with suitable crosslinking resins, such as aminoplast resins, to create coating vehicles which, upon curing by baking yield films which have both high hardness and high impact values. The enhanced properties are attributed to the L.C. interaction of the various polymer chains. A mesogen which is frequently used consists of the internal esters of two or more molecules of para-hydroxybenzoic acid (PHBA). This mesogen is connected to a polymeric polyol by esterification of the OH groups of the polyol with the residual carboxyl groups of the mesogen.
The L.C. polymers, while possessing good properties, have several drawbacks. First, the mesogenic groups are usually expensive to synthesize and incorporate into the polymer. For example, multiple PHBA end groups require a large quantity of PHBA and significantly increase the resin price. Second, the synthesis is complicated. In one method, the synthesis is based on the use of expensive and toxic dicyclohexylcarbodimide, which renders this method impractical from a commercial standpoint. Another method is based on direct esterification of PHBA with a polyesterdiol at 230.degree. C. in the presence of para-toluenesulfonic acid (p-TSA). Jones teaches that it is important that an acid catalyst be used and that the temperature be controlled to provide predominantly L. C. phenolic oligoesters. Polymers produced in accordance with the teachings of Jones result, however, in material with poor color, an unacceptably high loss of PHBA via decarboxylation, and a sizable loss of phthalic acid from the polymer due to anhydride formation. In order to be commercially attractive, it would be very desirable to provide the enhanced properties associated with Jones's L.C. polymers without the above-mentioned problems.
Efforts have been made to incorporate active phenolic functionalities into polymeric coating vehicles to enhance curing characteristics or the properties of the prepared coating. However, the coatings produced in accordance with the prior art are generally inferior or difficult to prepare.
U.S. Pat. No. 4,124,566 discloses the preparation of polyester resins based on the polyester reaction product of aromatic dicarboxylic acids and diols, including bisphenols, by a two stage reaction wherein an aromatic dicarboxylic acid is first esterified by reaction with an aromatic monohydroxy compound, followed by a second stage reaction of this esterification product with a bisphenol compound or a mixture thereof with an aliphatic diol or dihydroxy benzene. These resins are characterized as having superior thermal stability, transparency and chemical stability. Because of the high content of aromatic components, the flexibility of the resins is relatively low and the glass transition temperature is relatively high. They are also of relatively, high molecular weight as evidenced by high reduced viscosities in excess of 0.9 for the materials produced.
U.S. Pat. No. 4,028,111 discloses polyester polymers based on an alternating polymer of an aliphatic dicarboxylic acid such as adipic acid and a bisphenol such as bisphenol A prepared using an excess of bisphenol such that the bisphenol groups also end-cap the polyester. The free hydroxy group of the bisphenol end cap is then reacted with a compound having quinonediazide group to produce a light sensitive polymer.
U.S. Pat. No. 4,281,101 discloses the preparation of relatively high molecular weight polycarbonates comprising reacting a mixture of an aliphatic diol, a carbonic acid bis-aryl ester such as diphenyl carbonate and a diphenyl such as bisphenol A to produce a polycarbonate polymer containing diphenyl carbonate end groups of the diphenyl compound. These polymers may then be used as a precursor for further reaction with preferably aliphatic diols and phosgene to produce thermoplastic aliphatic-aromatic polycarbonate elastomers of high molecular weight. Similar polycarbonates are disclosed in U.S. Pat. Nos. 4,216,298 and 4,297,455.
U.S. Pat. No. 3,787,520 discloses a phenolic hydroxy terminated resin which may be used as a crosslinking agent in the preparation of dry powder paint systems based on crosslinkable copolymers of glycidyl methacrylate and an ethylenically unsaturated compound. The hydroxy terminated resin is prepared by reacting an epoxy compound with a diphenol such as bisphenol A to produce a polyether terminated by the diphenol. It is also known in the art to prepare phenol terminated liquid elastomers by reacting carboxyl terminated polymers of dienes with diphenols such as bisphenol A such that a phenolic hydroxyl group forms an end group in the polymer chain. These phenol terminated elastomers are subsequently used to cross link epoxy resins to produce an improvement in impact resistance. Examples of such systems are disclosed in U.S. Pat. Nos. 3,770,698 and 3,966,837.
U.S. Pat. No. 4,507,462 to Stille discloses biphenylene end-capped low molecular weight aromatic polymers and crosslinked versions thereof which may be prepared using a misbalanced polymerization reaction of a suitable aromatic amino ketone compound and a suitable aromatic ketomethylene compound, thereafter also adding a monofunctional biphenylene compound such as 2-acetylbiphenlene.
Various catalysts and catalyst systems have also heretofore been disclosed in the are for use in the preparation of mono- di- and polyester condensation products of organic acids and hydroxy-containing aromatic monomers. For example, U.S. Pat. No. 4,610,825 discloses the use of phosphorous acids or salts thereof as catalysts in the preparation of monoesters of a hydroxy aromatic compound such as phenol, and a carboxylic acid containing at least four carbon atoms, such as octanoic acid. Patentee indicates that the reaction product obtained is of high purity and low color.